macOS Format string is not a string literal.

[larswik]

When my program is not able to move a file to a different location I add the file name to an NSMutableArray. When the program finishes, and the array has a count of more the 0, I have an NSAlert display on the screen with a list of files that did not transfer. It works just fine, or as expected, but I get this warning. The part of the alert that takes the argument takes an NSString. I created an NSString but I get the error.

-(void)transferAlertError{
    NSString *myArrayString = [[canNotTransferArray valueForKey:@"description"]  componentsJoinedByString:@", "];
    
    NSAlert *alert = [NSAlert alertWithMessageText:@"Files not copied because of duplicate names." defaultButton:@"Ok" alternateButton:nil otherButton:nil informativeTextWithFormat:myArrayString];
    [alert setAlertStyle:NSInformationalAlertStyle];
    [alert runModal];
}

I did a Google search and found a number of these problems to figure it out first. I did try to use [NSString stringWithFormat"%@,] but it still gave me the same problem. I'm pretty sure it is a formatting issue but I just can't put my finger on it.

Any help at this point would be appreciated.

 

[ArtOfWarfare]

Your first line confuses me... You're getting the description of an array, which is a string. Then you're trying to join components together, but that doesn't make sense because you have a string at that point, not an array.

Can you give more details on your error? Is it occurring at runtime or compile time? Which line is the error occurring on?

 

[ohbrilliance]

componentsJoinedByString is an instance method of NSArray. Is the object returned by canNotTransferArray valueForKey"description" an instance of NSArray?

If not then componentsJoinedByString will return nil, probably not what you expected.

 

[lee1210]

The "informativeTextWithFormat:" argument expects a literal format string. The method then accepts variable arguments for the parameters that fill in placeholders. You're generating a formatted string and feeding it in. If you inadvertently passed format specifiers you'd have problems. The format @"%@" and your current string following it should do it.

-Lee

 

[gnasher729]

I did a Google search and found a number of these problems to figure it out first. I did try to use [NSString stringWithFormat"%@,] but it still gave me the same problem. I'm pretty sure it is a formatting issue but I just can't put my finger on it.

The last parameter is a format string, followed by optional parameters. Similar to printf. For example it could be:

informativeTextWithFormat"x = %d, y = %d", x, y

So the format string should be a string literal, to allow the compiler to check it. In this example, the compiler will see two %d in the string and check that there are two int values.

If it isn't a string literal, then you are in danger - if the string contains for example %d, then it will want an integer value to substitute for the %d, which most likely will produce rubbish. If the string contains %s or %@, then your program will most likely crash.

Passing in [NSString stringWithFormat... ] just gives the same problem again.

Pass as the last parameter:

informativeTextWithFormat"%@", myArrayString

 

[larswik]

Thanks guys, you pointed out something I didn't even notice. I was so focused on that it was an NSString and that was the parameter that I was providing.

informativeTextWithFormat:

I then 'READ THE DOCS' completely and the keyword "Format" jumped out at me, as in Format specifier. Which then the docs had a link, "For more information on format strings, see “Formatting String Objects”." and the examples you had made sense.

I revised my Method to this and now it works as expected with errors.

-(void)transferAlertError{
    NSString *myArrayString = [canNotTransferArray description];
    
    NSAlert *alert = [NSAlert alertWithMessageText:@"Files not copied because of duplicate names." defaultButton:@"Ok" alternateButton:nil otherButton:nil informativeTextWithFormat:@"%@", myArrayString];
    [alert setAlertStyle:NSInformationalAlertStyle];
    [alert runModal];
}

Thanks for the help folks....